what is determinanat of matrix i have a code i dont understand what is the logic behind

Does the explanation on Wikipedia help you?

If not, could you maybe rephrase your question to be more specific?

ok thats clear what about 4*4 matrix

they have given only upto 3*3 matrix

There are a few methods for finding the det of a matrix.

Here is an example for using the minors method.

they have given only upto 3*3 matrix

They also have a section on n*n matrices right after the one about 3*3.